Correction to: The BH3-only protein Bad is dispensable for TNF-mediated cell death.

Since publication of this article, the authors wished to draw attention to an error in the materials section as a result of which they have been mis-cited ( https://www.nature.com/articles/s41422-018-0041-7 ). The dose of TNF given was not in fact 15 mg/kg body weight (as stated in the "mouse work" section), but 15 µg/kg body weight.

Conditional knockdown of BCL2A1 reveals rate-limiting roles in BCR-dependent B-cell survival.

Bcl2 family proteins control mitochondrial apoptosis and its members exert critical cell type and differentiation stage-specific functions, acting as barriers against autoimmunity or transformation. Anti-apoptotic Bcl2a1/Bfl1/A1 is frequently deregulated in different types of blood cancers in humans but its physiological role is poorly understood as quadruplication of the Bcl2a1 gene locus in mice hampers conventional gene targeting strategies. Transgenic overexpression of A1, deletion of the A1-a paralogue or constitutive knockdown in the hematopoietic compartment of mice by RNAi suggested rate-limiting roles in lymphocyte development, granulopoiesis and mast cell activation. Here we report on the consequences of conditional knockdown of A1 protein expression using a reverse transactivator (rtTA)-driven approach that highlights a critical role for this Bcl2 family member in the maintenance of mature B-cell homeostasis. Furthermore, we define the A1/Bim (Bcl-2 interacting mediator of cell death) axis as a target of key kinases mediating B-cell receptor (BCR)-dependent survival signals, such as, spleen tyrosine kinase (Syk) and Brutons tyrosine kinase (Btk). As such, A1 represents a putative target for the treatment of B-cell-related pathologies depending on hyperactivation of BCR-emanating survival signals and loss of A1 expression accounts, in part, for the pro-apoptotic effects of Syk- or Btk inhibitors that rely on the 'BH3-only' protein Bim for cell killing.

The BH3-only protein Bad is dispensable for TNF-mediated cell death.

Tumor necrosis factor (TNF) is a key signaling molecule orchestrating immune and inflammatory responses and possesses the capacity to trigger apoptotic as well as necroptotic cell death. Apoptotic cell death elicited by TNF has been demonstrated to engage pro-apoptotic Bcl-2 family proteins, most prominently the BH3-only protein Bid, a key substrate of caspase-8, the key effector protease downstream of TNF receptor I. Most recently, the BH3 domain-containing protein Bad (Bcl-2-antagonist of cell death) has been shown to be rate limiting for TNF-mediated cell death, suggesting possible synergy with Bid, but genetic analyses presented here demonstrate that it is dispensable for this process.

PARP-2 sustains erythropoiesis in mice by limiting replicative stress in erythroid progenitors.

Erythropoiesis is a tightly regulated process in which multipotential hematopoietic stem cells produce mature red blood cells. Here we show that deletion of poly(ADP-ribose) polymerase-2 (PARP-2) in mice leads to chronic anemia at steady state, despite increased erythropoietin plasma levels, a phenomenon not observed in mice lacking PARP-1. Loss of PARP-2 causes shortened lifespan of erythrocytes and impaired differentiation of erythroid progenitors. In erythroblasts, PARP-2 deficiency triggers replicative stress, as indicated by the presence of micronuclei, the accumulation of γ-H2AX (phospho-histone H2AX) in S-phase cells and constitutive CHK1 and replication protein A phosphorylation. Transcriptome analyses revealed the activation of the p53-dependent DNA-damage response pathways in PARP-2-deficient cells, culminating in the upregulation of cell-cycle and cell death regulators, concomitant with G2/M arrest and apoptosis. Strikingly, while loss of the proapoptotic p53 target gene Puma restored hematocrit levels in the PARP-2-deficient mice, loss of the cell-cycle regulator and CDK inhibitor p21 leads to perinatal death by exacerbating impaired fetal liver erythropoiesis in PARP-2-deficient embryos. Although the anemia displayed by PARP-2-deficient mice is compatible with life, mice die rapidly when exposed to stress-induced enhanced hemolysis. Our results pinpoint an essential role for PARP-2 in erythropoiesis by limiting replicative stress that becomes essential in the absence of p21 and in the context of enhanced hemolysis, highlighting the potential effect that might arise from the design and use of PARP inhibitors that specifically inactivate PARP proteins.

Increased leukocyte survival and accelerated onset of lymphoma in the absence of MCL-1 S159-phosphorylation.

The antiapoptotic BCL-2 protein MCL-1, which opposes mitochondrial outer membrane permeabilization, was shown to have a crucial role in the survival of hematopoietic cells. We have previously shown that, upon loss of phosphatidylinositol 3-kinase signaling, S159 of MCL-1 is phosphorylated by glycogen synthase kinase-3 (GSK-3), earmarking MCL-1 for enhanced ubiquitylation and degradation. In this study, we introduced MCL-1(wt) or the phosphorylation-deficient mutant MCL-1(S159A) in mouse BM cells, followed by adoptive transfer to recipient mice. Mice expressing MCL-1(S159A) exhibited significantly elevated white blood cell and lymphocyte counts, whereas no effect was observed on the distribution of T and B lymphocyte subsets or the numbers of monocytes, red blood cells or platelets. Expression of MCL-1(S159A) in Eµ-Myc transgenic bone marrow significantly accelerated the onset of disease, and these mice displayed increased spleen weights compared with Eµ-Myc/MCL-1(wt) mice. Our data demonstrate that the absence of MCL-1 S159 phosphorylation provides a survival advantage for hematopoietic cells in vivo and facilitates oncogenesis.

Molecular analysis of neutrophil spontaneous apoptosis reveals a strong role for the pro-apoptotic BH3-only protein Noxa.

Neutrophils enter the peripheral blood from the bone marrow and die after a short time. Molecular analysis of spontaneous neutrophil apoptosis is difficult as these cells die rapidly and cannot be easily manipulated. We use conditional Hoxb8 expression to generate mouse neutrophils and test the regulation of apoptosis by extensive manipulation of B-cell lymphoma protein 2 (Bcl-2)-family proteins. Spontaneous apoptosis was preceded by downregulation of anti-apoptotic Bcl-2 proteins. Loss of the pro-apoptotic Bcl-2 homology domain (BH3)-only protein Bcl-2-interacting mediator of cell death (Bim) gave some protection, but only neutrophils deficient in both BH3-only proteins, Bim and Noxa, were strongly protected against apoptosis. Function of Noxa was at least in part neutralization of induced myeloid leukemia cell differentiation protein (Mcl-1) in neutrophils and progenitors. Loss of Bim and Noxa preserved neutrophil function in culture, and apoptosis-resistant cells remained in circulation in mice. Apoptosis regulated by Bim- and Noxa-driven loss of Mcl-1 is thus the final step in neutrophil differentiation, required for the termination of neutrophil function and neutrophil-dependent inflammation.

Bcl-2-regulated cell death signalling in the prevention of autoimmunity.

Cell death mediated through the intrinsic, Bcl-2-regulated mitochondrial apoptosis signalling pathway is critical for lymphocyte development and the establishment of central and maintenance of peripheral tolerance. Defects in Bcl-2-regulated cell death signalling have been reported to cause or correlate with autoimmunity in mice and men. This review focuses on the role of Bcl-2 family proteins implicated in the development of autoimmune disorders and their potential as targets for therapeutic intervention.